1. Field of the Invention
The present invention relates in general to optical oscillators and phase modulators and relates in particular to optical phase oscillators that produce a continuous wave digital phase output.
2. Discussion of Related Art
Oscillators are well-known in electronics and are essential components for synchronizing interconnected circuits. Oscillators are used primarily as system clocks to synchronize the activities of interacting circuits. Most electronic circuits rely on a crystal to provide oscillations for a system clock.
Typically, optical circuits rely on generated pulses from a laser resonator to form an oscillating signal. Electrical pulses are used to power a laser resonator for creating optical pulses, or a saturable absorber is used in a laser resonator to release pulses greater than a threshold value.
However, phase optical circuits are becoming a viable alternative to pulsed optical circuits and require a phase oscillating signal for complex circuits. Several methods exist for creating a phase oscillator.
In one method, an electro-optic effect is used to alter the optical phase delay of a waveguide through which an optical signal travels. An electric signal is oscillated which induces a corresponding oscillating e change of the optical signal in the waveguide. However, this method is slower than an all-optical method due to the speed of the electro-optic effect and the speed limitations of oscillating an electrical signal.
A similar method based on optical intensity dependent phase changes, resulting from refractive index changes, has been developed. This method uses a pulsed optical signal to change the refractive index of a waveguide through which a continuous wave optical signal travels. This method is also slower than a dedicated phase oscillator due to the speed and magnitude of the refractive index changes.
Another method employs an optical phase logic gate with a feedback signal for generating an oscillating signal. However, the logic gate provides unused functionality and unnecessary circuitry that results in an oscillation cycle time greater than the cycle time of a dedicated oscillator device.
Dedicated all-optical phase oscillators provide better phase oscillating output signals than the methods described above.
In an all-optical method, the symmetric on/off cycle output pulses from a light pulse generator are converted to continuous wave phase oscillating signals by combining the pulses with a continuous wave beam that is half the magnitude of and opposite in phase to the pulses. However, this method is more complex to design and operate than a phase oscillator which uses only a phase signal because phase matching is required.
In U.S. Pat. No. 5,555,126, Hait describes a phase oscillator that uses special interference to transfer all of the input energy into the output signal. The oscillator design uses feedback, but does not include a specification for an integrated optic design. Also, the output signal is generated only when the input signal is present. The output signal power is obtained directly from the input signal.
Optical phase modulated circuits are becoming more prevalent and more useful in optics. A simpler and more easily manufactured optical phase oscillator is necessary. It is, therefore, an object of the present invention to provide such a phase oscillator.